This invention involves a diagnostic system for a ballast of a high-pressure gas discharge lamp for a motor vehicle, having a light control module, which connects the ballast to an operating voltage source and monitors current reception of the ballast, and with the ballast, having: a voltage converter for supplying voltage to the high-pressure gas discharge lamp, a safety circuit for recognizing fault functions of the ballast and the high-pressure gas discharge lamp and turning the voltage converter off in case of a fault, and a diagnostic circuit for generating a fault signal in case of a fault.
Increasingly in more and more motor vehicles, illumination devices are being switched on or off via a light control module. A light control device for a motor vehicle is disclosed in DE 43 41 058 C1, with this example showing that a device of this type can be very complex. That is, here both a light control module as well as a lamp module are structured as "intelligent" structural assemblies, i.e. provided with a microcomputer, such that this type of light control device is quite expensive. Particularly in motor vehicle technology, however, constructions of light control devices that are especially simple are preferred for cost reasons.
For the most part, a light control module has a device for current control, which indicates to a vehicle driver, if incandescent lamps are controlled for example, whether an incandescent lamp must be changed. This is problematic in the control of high-pressure gas discharge lamps, which are increasingly used in motor vehicles, since they are driven by a ballast. In high-pressure gas discharge lamps, the light control module can not namely distinguish whether the lamp or its associated ballast is defective. Thus, it is advantageous, if the ballast takes over the diagnostics and transmits data to the light control module.
Standard commercial ballasts for high-pressure gas discharge lamps, for example such as those of the assignee, have for this purpose a diagnostic output, which is connected to the light control module via a diagnostic line. The cable expense for an additional diagnostic line per ballast thus causes additional costs, and this is also true for structural components for the output of diagnostic signals (output drivers, possibly even a microprocessor) within the ballast, with these additional costs accruing even if the diagnostic possibility is not to be used in a motor vehicle.
It is thus an object of this invention to create a diagnostic system for a ballast of a high-pressure gas discharge lamp in a motor vehicle, which is especially uncomplicated and inexpensive in structure.